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DC-9 Redesigned Cabin Pressure Outflow Valve
When i was looking at one of northwests refurbished DC-9s it shocked me that the standard dc-9 / md-80 outflow valve was gone replaced with one a rectangular one that resembled the 717. is this part of their refurbishment, is the old style valve such a bad design that it warrented a totally new design, the old style was used up through the md-90 so i don't see it as a bad design?
RE: DC-9 Redesigned Cabin Pressure Outflow Valve
Very good observation.
It looks like they modified their DC9s to an electric type of outflow valve assembly, as compared to the mechanical type normally used. This is of course unless it was an option on the DC9 (I don't know that much about the DC9). But I'm making an assesment based on the pictures I have seen.
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Photo © Joseph J. Wagner
Here is a picture of a NW DC9 with the standard butterfly and nozzle outflow valve assy).
View Large View Medium
Photo © Aric Thalman
Here is a picture of the throttle quadrant of a NW DC9 wth that type of outflow valve system. Maybe someone can confirm, but by the looks of it, some DC9s didn't have an Automatic Cabin pressurization system. It looks like this one can only be controlled manually. I know the MD80s have auto, but the control looks alot different in the flightdeck. There is a control "wheel".
View Large View Medium
Photo © Christian Mogensen
Here is a NW DC9 with the "Boeing" type of outflow valve.
View Large View Medium
Photo © Stephen Dobbins
Here is the throttle qudrant of a DC9 with the control area for the outflow valve blocked off. If the valve control is still mechanical (which I doubt), then they moved the control elsewhere. But it makes more sense that they modified it to the electric type of outflow valve control.
Was the old design a bad design?? I guess it depends on who u talk to. I've heard that on many occasions of items getting caught in the outflow valve assy causing many pressurization problems.
The Boeing design is a much simpler design. There isn;t as much "monkey motion" as there is with the butterfly/nozzle type.
It looks like they modified their DC9s to an electric type of outflow valve assembly, as compared to the mechanical type normally used. This is of course unless it was an option on the DC9 (I don't know that much about the DC9). But I'm making an assesment based on the pictures I have seen.
Photo © Joseph J. Wagner
Here is a picture of a NW DC9 with the standard butterfly and nozzle outflow valve assy).
Photo © Aric Thalman
Here is a picture of the throttle quadrant of a NW DC9 wth that type of outflow valve system. Maybe someone can confirm, but by the looks of it, some DC9s didn't have an Automatic Cabin pressurization system. It looks like this one can only be controlled manually. I know the MD80s have auto, but the control looks alot different in the flightdeck. There is a control "wheel".
Photo © Christian Mogensen
Here is a NW DC9 with the "Boeing" type of outflow valve.
Photo © Stephen Dobbins
Here is the throttle qudrant of a DC9 with the control area for the outflow valve blocked off. If the valve control is still mechanical (which I doubt), then they moved the control elsewhere. But it makes more sense that they modified it to the electric type of outflow valve control.
Was the old design a bad design?? I guess it depends on who u talk to. I've heard that on many occasions of items getting caught in the outflow valve assy causing many pressurization problems.
The Boeing design is a much simpler design. There isn;t as much "monkey motion" as there is with the butterfly/nozzle type.
RE: DC-9 Redesigned Cabin Pressure Outflow Valve
thanks for the response i was in louisville training some people, and happend to look at one of NWs DC-9s and kept lookuing and was like "this isnt right"
RE: DC-9 Redesigned Cabin Pressure Outflow Valve
A mod program was put in place 3 or 4 yrs ago to go with electric control of the outflow valve.This for pax comfort and ease of maintance.
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